The present invention relates to a brushless motor-driving circuit and a portable terminal incorporating this circuit. More particularly, the invention relates to a driving circuit of a so-called sensorless-type brushless motor having no position sensor for detecting the rotating position of a rotor and a portable terminal exemplified by a portable telephone incorporating such a brushless motor-driving circuit.
There has been disclosed a sensorless-type brushless motor-driving circuit designed to generate a power on/off signal upon detection of a counter-electromotive voltage in a motor-driving coil during a power-off period. This type of circuit forms a phase-control loop or a speed-control loop in a manner maintaining a constant phase relation or a steady speed relation, thereby driving a brushless motor without recourse to position sensors (as disclosed in Japanese Patent No. 2892164).
The sensorless-type brushless, motor-driving circuit above uses a phase-detection amplifier (corresponding to the power logic detector in the above-cited patent) to detect the phase of a counter-electromotive voltage generated by coils having different phases during constant revolutions (the phase of the counter-electromotive voltage represents a point of changeover to a median voltage). The phase-detection provides a basis for determining when to turn on the next output stage. Where there is a fluctuation in motor load leading to changes of the phase of the counter-electromotive voltage, the rotating speed is controlled correspondingly so that the brushless motor is driven in a stable manner. Since there is no need for position sensors, this brushless motor-driving circuit is small, inexpensive, and used extensively in rotation-driving applications today.
One disadvantage of the sensorless-type brushless motor-driving circuit above is that it is vulnerable to noises generated by the motor itself and noises produced by peripheral IC components operating on the same power-supply line as the driving circuit. Such noises can hinder the phase-detection amplifier from correctly detecting the phase of the counter-electromotive voltage.
To suppress the adverse effects of these noises requires installing noise filters each made up illustratively of a capacitor and a resistor upstream and downstream of the phase-detection amplifier and with regard to each of the phases involved. A high level of offset accuracy is required of the phase-detection amplifier. Where the driving circuit is to be implemented in IC form, the components (capacitor and resistor) corresponding to each of the phases constituting the filter upstream of the phase-detection amplifier need to be attached externally. This means there must be more components to be connected externally to the IC package. The filter downstream of the phase-detection amplifier needs to be incorporated in the IC chip. The circuit structure thus becomes complicated and results in a greater required circuit area.
To detect the phase of the counter-electromotive voltage obviously requires installing the phase-detection amplifier. When the driving circuit is implemented in IC form, an extensive chip area must be devoted to such circuits as the phase-detection amplifier and a driving waveform generator using that amplifier.
It is an object of the present invention to provide a brushless motor-driving circuit of an appreciably simplified circuit structure capable of stable rotation drive free from the adverse effects of noises generated by the motor itself or by peripheral IC components operating on the same power-supply line as the driving circuit and a portable terminal incorporating such a brushless motor-driving circuit.
In carrying out the invention and according to one aspect thereof, there is provided a brushless motor-driving circuit including: an initializing element setting an initial rotating speed; an oscillating element for generating a frequency corresponding to the initial rotating speed set by the initializing element; a frequency-controlling element for causing the frequency generated by the oscillating element to change from the frequency corresponding to the initial rotating speed to a frequency corresponding to a constant rotating speed; a driving-signal-generating element for generating driving signals having a plurality of phases based on the generated frequency of the oscillating element; and a driving element for driving coils having a plurality of phases based on the driving signals having the plurality of phases generated by the driving-signal-generating element. This brushless motor-driving circuit is used as a motor-driving circuit for driving a vibrating motor in a portable terminal exemplified by a portable telephone. Typically, the portable telephone utilizes the motor-driving circuit to drive the vibrating motor of a vibrator that announces an incoming call through vibrations.
In the brushless motor-driving circuit of the above structure or in the portable terminal incorporating that circuit, the oscillating element outputs, upon activation of the brushless motor, a generated frequency corresponding to the initial rotating speed set by the initializing element. In turn, the driving-signal-generating element generates driving signals having a plurality of phases based on the generated frequency. The driving signals with the plurality of phases allow the driving element to drive coils having a plurality of phases, prompting the brushless motor to start rotating. With the motor thus started, the frequency-controlling element causes the generated frequency to change from the frequency corresponding to the initial rotating speed to a frequency corresponding to a constant rotating speed. Under such a frequency-controlled synchronizing scheme, the motor""s revolutions reach the constant rotating speed and stay there.
Other objects, features and advantages of the invention will become more apparent upon a reading of the following description and appended drawings.